1. Field of the Invention
The present invention relates to stilbene-based materials, their preparation and their use for the preparation of materials which can be structured by means of light.
2. The Prior Art
Examples of familiar materials which can be structured by light in the visible range are azo dyestuffs. Fields of use for such materials are, inter alia, information storage and optical elements which can be structured by means of light, such as, for example, holographic, optical elements.
Colored materials are unsuitable for various uses since the intrinsic color represents a limitation to the usable spectral range. Materials without absorption bands in the visible spectral range but with absorption bands in the UV or IR range are preferably used for colorless optical elements.
Merocyanines, fulgides and spiropyrans, for example, are used in the near infrared range. The known materials for optical elements which have absorption bands in the infrared range do not guarantee a high number of writing-erasing cycles since the dyestuffs are not stable in the long term (Fabian, Chem. Rev. 1992, 1197). Furthermore, many of these so-called infrared dyestuffs additionally have absorption bands at shorter wavelengths and therefore do not appear completely colorless.
Colorless devices can in principle also be realized by materials having absorption bands exclusively in the near UV range from 250 to 380 nm. Such devices have the advantage that information stored is not erased again by visible light. Furthermore, the storage density which can be achieved using light of shorter wavelength for writing in the information is significantly higher. However, the choice of dyestuffs is very limited here. Possible photochromic compounds here are primarily stilbenes. Stilbenoid compounds, however, have some side reactions which have already been known for a long time, such as, for example, cyclization to dihydrophenanthrene derivatives (with subsequent oxidation to phenanthrene) or dimerization to cyclobutanes. It has therefore not been possible to date for them to be used for optical information storage (L. Feringa, Tetrahedron, 1993, 8267-8310, H. Meier, Angewandte Chemie, Volume 31, No. 11, November 1992, pages 1399-1540).